Measuring and control apparatus



Jan. 20, 1942. s JONES 2,270,732

MEASURING AND CONTROL APPARATUS Filed May 22, 1940 2 Sheets-Sheet 1 INVEN TOR. HARRY S. JONES v Jan. 20; 1942.

H. s. JONES 2,270,732,

MEASURING AND CONTROL APPARATUS Filed May 22, 1940 2 Sheets-Sheet 2 FIG.6.

INVENTOR. I HARRY s. JONES a V I AT NEY Patented Jan. 20, 1942 UNITEDSTATES PATENT OFFICE MEASURING AND CONTROL APPARATUS Harry S. Jones,Philadelphia, Pa., assignor to The Brown Instrument Company,Philadelphia, Pa.,

a corporation of Pennsylvania Application May 22, 1940, Serial No.336,520

29 Claims.

The present invention relates to improvements in instruments for makingelectrical measurements and particularly to a method of and apparatusfor rendering such instruments extremely stable in operation.

A general object of the invention is to provide an. effective method ofand apparatus for regulating a measurable condition such as mechanical,electrical, physical, etc.', in such a manner as to prevent hunting.

A special object of the invention is to provide an improved method ofand apparatus for measuring the moisture content of solid bodies such astextile, paper, and other sheets or webs, and the invention comprisesfeatures especially devised and adapted for use in measuring themoisture content of a moving web of material by measuring the electricalconductivity of the web.

For purposes of illustration, I have shown and hereinafter described indetail, the use of various forms of embodiment of the present inventionin measuring the moisture content of a travelling web of warp yarn atthe end of a sizing operation to which the yarn is subjected preparatoryto its use in a weaving loom. It has been found necessary in themanufacture of woven fabrics by high speed weaving methods to conditionthe yarn so as to increase the strength thereof, or to increase itsresistance to the friction or chafing to which it is subjected in theweaving operation, and such conditioning is commonly efiected bysubjecting the yarn to a sizing or so-called "slashing treatment.

That treatment consists in the application to the yarn of a solutioncomposed of suitable in gredients forming a protective coating on theyarn and its fibrous constituents and softening the threads to make themsufficiently pliable to bend about the filling threads in the wovengoods. In the slashing operation it has been found that the best resultsare obtained when the sizing is applied to the warp after the latter hasbeen wound on a warp beam, and while it is being unwound from the warpbeam and wound up on a loom beam, as the final step in the preparationof the warp for insertion in the loom. In so slashing or sizing warpyarn it is desirable that the sized warp yarn, when wound on the loombeam should be at a suitably low temperature, and should have a'moisturecontent, within a small range of variation, and much less than themoisture content of the yarn as it passes away from the sizing bath. Toreduce the moisture content of the yarn as it passes away from thesizing bath, the yarn is moved over steam heated drying drums or rolls,and is then cooled by passing it over a cooling roll.

The proper operation of the-slashing machine is greatly facilitated byan accurate measurement of the moisture content in the web as it passesfrom the slasher proper to the loom beam on which it is wound, not onlybecause the moisture content must be closely controlled, but alsobecause in the operation of a properly designed slasher the maintenanceof a suitable moisture content insures against risk of overheating thedrying rolls and resultant burning or injuring of the warp yarn. Thatthe range of variation in the moisture content of the warp should benarrow is practically essential, because a certain small moisturecontent in the yarn is desirable to permit evaporative cooling of theyarn and resultant dissipation of heat in the weaving operation, whileamoisture content, but little greater than that required for the desiredevaporative cooling action may result in the mildewing or discolorationof the fabric produced, and is otherwise objectionable in the weavingoperation.

Heretofore various devices have been proposed for measuring the moisturecontent of webs and other substances in terms of electricalconductivity, one such form being disclosed in a copending applicationSerial No. 134,092 filed March 31, 1937, by Walter P. Wills forMeasuring and control apparatus and now issued into Patent No,2,215,805. The prior art devices, however, have been subject toinstability of operation under conditions of rapid conditionfluctuations because of their inability to distinguish between averageand instantaneous changes in moisture content of the web undermeasurement, without requiring adjustments of the measuring instrumentswhich render them sluggish in operation. For many purposes the importantmeasurements of the moisture content of a web, are not measurements ofthe moisture contents of small individual portionsof the web, but aremeasurements of the average web moisture con-- the trend of changes inthe average moisture content or a moving web of material in which anextremely sensitive measuring instrument may be employed, 1

The various features of novelty which characterize my invention arepointed out with particularity inthe claims'annexed to and forming apart of this specification. For a better understanding of the invention,however, its advantages and specific objects attained with its use,reference should be had to the accompanying drawings and descriptivematter in which I have illustrated and described a preferred embodimentof the invention.

Of the drawings:

Fig. 1 is a diagrammatic representation of a warp sizing or slashermachine, and means associated therewith in accordance with the presentinvention for measuring the moisture content of the yarn after it haspassed over the drying and cooling rolls of the slasher;

Fig. 2 is a schematic diagram illustrating a motor control circuit forautomatically varying the supply of steam to the slasher drying drums tothereby vary their web drying action:

Fig. 3 is a schematic representation of one form of electrical measuringcircuit adapted to be used in the Fig. 1 arrangement and embodying theinvention;

Figs. 4-6 illustrate modifications of the Fig. 3 arrangement; and

Fig. 7 illustrates a modification or the control circuit of Fig. 2.

In Fig. 1 I have illustrated the use of my invention in measuring theelectrical conductivity of a web of sized warp yarn as it leaves asizing machine or slasher" of conventional type. In the slasher shown inFig. 1, the warp l is unwound i'rom a warp beam 2 and is passed from thelatter through a sizing bath in a sizing pan I over so-called squeezerolls 4 to drying drums 5 whence the yarn passes over guide rolls 6 anda cooling drum I back of the final guide roll 6 onto a loom beam 8. Thedrying rolls 5 are heated by steam supplied through a pipe 9 at a rateregulated by a control valve It the adjustment of which is effectedautomatically by means to be described in accordance with the moisturecontent of the warp yarn. The moisture content or the warp yarn as itpasses from the slasher proper to the warp beam 8 is measured bymeasuring the electrical conductivity of the warp yarn as it passes overthe final guide roll Q 01 the slasher.

To measure the electrical conductivity of the warp passing over thefinal guide roll 6, I employ an electrode or contact in the form of aconducting roll I] which is held in contact with'the warp passingbetween it and the final guide roll 8 by a suitable bias force, due, asshown, partly to gravity and partly to spring action. The guide roll Iis connected to ground in ordinary practice, as a result of thegrounding of the slasher frame in which the guide roll is journalled.The roll II is connected by a conductor II to a measuring circuit deviceI3 having a ground connection at II and means for amplifying variationsin the current which flows through and varies with the conductivity ofthe warp passing between the roll H and adjacent roll The currentamplifled by the device I 3 is measured by an electrical measuringinstrument Ii which may be of any suitable type. and as shown is a"Brown potentiometer control 'instrument or commercial type, one form ofwhich is disclosed in the Harrison Patent 1,946,280 issued February 6,1934. When the instrument II is a control instrument it may includeprovisions for automatically adjusting the operation of the slasher asrequired to maintain the moisture content of the warp in engagement withthe contact roll H at an approximately constant predetermined value, orthe measurements turnished by the instrument l5 may be utilized in themanual control of the slasher operation.

In controlling the operation of the slasher so as to maintain a constantmoisture content in the warp being wound on the loom beam 8 the supplyof steam to the drying rolls 5 may be kept constant and the speed oftravel of the warp over the drying rolls varied as required or, asillustrated in Fig. 1, the speed of travel of the warp may be keptconstant and the supply oi steam to the drying rolls varied. I prefer toopcrate the slasher in accordance with the latter method inasmuch asgreater insurance is then had that the amount of size taken up by eachshort longitudinal section of the warp will remain constant.

In Fig. 2 I have illustrated one form of means for controlling theadjustment of the steam valve l0 under control of the measuring circuitdevice l3 described in detail hereinafter and thereby in accordance withthe moisture content of the warp. As illustrated, a reversible seriestype electrical motor I5 is provided for adjusting the valve I0, whichmotor is energized from electrical current supply conductors L and L andis selectively controlled for operation in one direction or the other bythe closure'of one or the other of two control switches I! and IIconnected in circuit with a forward winding 19 and a reverse winding 20of the motor, respectively.

In operation when the moisture content 0! the warp yarn engaging thecontact roll H is greater than that desired, the switch I1 is closed andthe motor It then operates in the direction to increase the supply 01'steam to the drying rolls 5 and thereby to increase the drying action ofthe rolls 5 on the warp yarn. Conservely, when the moisture content ofthe warp engaging the contact roller H is less than that desired, the

switch 18 is closed and the motor It operates in the direction todecrease the supply of steam to the drying rolls 5 and thereby decreasethe warp drying eil'ect of the rolls 5.

The electrical measuring circuit included in the device l3 may takevarious forms, some of which are illustrated more or lessdiagrammatically in Figs. 3-6. The circuit arrangement shown in Fig. 3comprises a balanced Wheatstone bridge 2!, one arm of which includes theresistance of the web whose moisture content is being measured and theother arms of which include resistances 22, 23 and 24, the latter ofwhich is shunted by a resistance 25 and a condenser 26 connected inseries and the purpose of which is explained hereinafter.

A standardizing resistance 23a may desirably be provided in the bridgenetwork arm including the resistance 23. Energizing current is suppliedthe bridge network 2| from a suitable source of direct current, forexample, from a battery 21 having its terminals connected through anadjustable resistance 28 to the opposed bridge Junctions 29 and 30. Theopposed normally equipotential junctions comprising a ilxed junction 31and the point of engagement of a contact 32 with the resistance 22 areconnected by conductors 34 and 35 to the terminals of a galvanometer 33having a resistance 38 connected in shunt therewith. As shown the conductor 35 is connected to one end oi resistance 36 and the cgnductor 34,in which a resistance 31 is inserted, is connected to a contact 38 whichcontact may be manually adjusted along resistance 36 for varying thesensitivity of'the galvanometer. A resistance 39 is connected in thebridge arm including the web under measurement and is desirably providedto permit the measurement of lower values of web-resistance and toprotect the galvanometer 33 from damage in the event of the contact rollbeing connected directly to ground. The standardizing resistance 23areferred to above is provided to calibrate the instrument so that, whenthe resistance between the contact roll i I and the roll 6 is zero, thebridge network 2| will be balanced with the contact 32 in its lowestposition as seen in Fig. 3.

In operation with the normal balanced condition of the Wheatstone bridgecircuit 2|, the bridge junctions 3| and 32 will be at the same potentialand the pointer 43 of the galvanometer 33 will then be in its neutral orzero poslsponding direction. Conversely, an increase in f the moisturecontent of the warp in contact with the roll Ii and the resultantreduction in the value of the warp resistance increases the potential ofthe junction 3| with respect to the junction 32 to cause a deflection ofthe galvanometer pointer 43 in the opposite direction.

The pointer 40 of the galvanometer will deflect in one direction or inthe opposite direction from its neutral position as the potential of thebridge junction 3| rises above or falls below'the potential of thejunction 32 and the deflectlve position of the pointer 43 might berelied upon to furnish an indication of the magnitude of the moisturecontent of. the warp, or extent of its departure from a predeterminedvalue thereof, if the circuit included no rebalancing provisions,

, such predetermined value being determined by the existing adjustmentof resistor, 23a. A more accurate measure of the moisture contentvariation is furnished in the circuit shown'in Fig. 3 by the position ofthe movable contact 32 when the latter is adjusted as required torebalance the bridge following any change in the warp moisture contentand value of the warp resistance.

When the bridge network 2| is unbalanced as a result of a decrease inthe moisture content of the warp and consequent increase inthe warpresistance making the potential of the junction 3| lower than that ofthe junction 32, the bridge may be rebalanced by adjusting the contact32 in an upward direction as seen in Fig. 3. Con-- versely, when thebridge is unbalanced as a result of an increase in the warp moisturecontent and resultant reduction in the valueof the warp resistancemaking the potential of the bridge junction 3| higher than that of thejunction 32, the bridge may be rebalanced by a suitable adjustment ofthe contact 32 in a downward direction.

Preferably the contact 32 is automatically adjusted as required torebalance the bridge. In obtaining this end, the galvanometer 33 isadapted on deflection of its pointer 43 in one direction or the otherfrom its normal neutral, or zero position, to energize a reversibleelectrical motor 4| for operation in one direction or in the oppositedirection. As diagrammatically shown, the motor 4| comprises a rotatablearmature 42 and separat forward and reverse windings 43 and 44respectively, each connected at one end through the armature 42- to anelectrical current supply conductor L The cooperating supply conductorI! is connected to the galvanometer pointer which engages the second endof and thereby energizes one or the other of the windings .43 and 44 onthe deflection of the pointer in one direction or the other from itsneutral, or zero position. The armature 42 drives a threaded shaft 45through suitable gearing not shown, which shaft carries a nut 46 whichis adjusted longitudinally of the shaft when the latter is rotated. Thenut 46 carries the contact 32. On the assumption that a decrease in thewarp moisture content results in a counter-clockwise deflection of thepointer 40 bringing the latter into engagement with a terminal ofwinding 43, the motor 4| then operates in the direction to adjust thecontact 32 in an upward direction. Conversely,- on an increase in thewarp moisture content and the clockwise deflection of the pointer 43from its neutral position into engagement with a terminal of winding 44,the motor is then set into rotation in the direction to rebalance thebridge by adjustingthe contact 32 in a downward direction.

As will be apparent the motor 4| may be suitably connected to controlswitches i1 and I! which may be identical to the correspondinglyidentified parts of Fig. 2 and made to operate -one or the other of thecontrol switches into closed position while simultaneously effectingbalancingadjustments of the contact 32 along the resistance 22 tothereby eifect variations in the supply of steam to the drying rolls 5and hence to eflfect variations in the web drying effect of the rolls.In Fig. 3 the control switches ill and I3 have been shown as mounted ona value, one or the other of the control switches will be actuated intoits closed position and a corresponding adjustment of the web dryingeffect of the rolls will be'efl'ected to restore the moisture content tosaid value. Disc 41 may be adjusted relative to armature 42 in anysuitable manner to determine the desired control value.

.For example, when the warp moisture content becomes greater than isdesirable. the motor It will be energized for rotation in the properdirection to effect a downward balancing adjustment of the contact 32 asseen in Fig. 3 and to simultaneously cause rotation of the disc 41 in aclockwise direction for actuating the switch increase in the supply ofsteam to the drying rolls 5, resulting in a decrease in moisture contentof the warp. Conversely, closure of the switch l8 will cause a decreasein the supply of steam to the drying rolls and thereby result in ahigher value of moisture content in the warp.

In lieu of the relay mechanism including the galvanometer controlledreversible motor 4| shown in Fig. 3 other forms of galvanometercontrolled relay mechanisms may be employed to automatically adjust thecontact 32. Thus,

for example, when the potentiometer I is of the Brown potentiometer"type, comprising a mechanical relay mechanism, including as itsactuating element a constantly rotating shaft which intermittentlyrebalancesa potentiometer circuit in response to deflection of theinstrument galvanometer associated with that circuit, the instrument canbe used without change other than in its circuit connections to effectthe slide wire resistance adjustment purposes effected in Fig. 3 by theuse of the galvanometer controlled motor 4|.

In order to permit the use of an extremely sensitive galvanometer 33 andat the same time render the network insensitive to instantaneous changesin moisture content of the warp, for example, changes due to varyingmoisture contents of small individual portions of the warp, means havebeen provided in the form of the resistance and condenser 26 shuntedacross the bridge arm including the resistance 24 in the arrangement ofFig. 3. With the moisture content of the warp at a given value thecondenser 26 will be charged to a corresponding extent and, due to theaction of resistance 25 which permits only slow leakage of the chargetherefrom, or slow charging thereof, tends to maintain that charge.Thus, if instantaneous-variations in the warp resistance occur, acorresponding bridge unbalance effect will not occur due to the actionof resistance 25 and condenser 26, and the galvanometer 33, althoughextremely sensitive, will not respond to such changes. If the change inwarp resistance persists, however, the condenser 26 will charge ordischarge accordingly as the warp resistance increases or decreases, andthereby permit an unbalancing action of the bridge network to which thegalvanometer 33 responds substantially instantaneously. The extent towhich the condenser 26 delays the response of the system to changes inwarp moisture content may be varied by adjustment of the value ofresistance 25, which, as

shown, is adjustable.

It is noted that subsequent adjustment of the contact 32 relatively tothe resistance 22 produced as a result of deflection of the galvanometerpointer is effective immediately to rebalance the bridge network and isnot subject to the delayed action introduced by the resistance 25 andcondenser 26. Thus, in effect, means have been provided for renderingthe system insensitive to instantaneous changes in the warp moisturecontent without sacrificing any sensitivity of the galvanometer 33. Thisfeature is to be especially noted because one drawback of prior artattempts to solve this problem has been the sacrifice ofgalvanometersensitivity.

The embodiment of the inventiondisclosed in Fig. 4 is similar to thatjust described except that an alternative arrangement has been shown foraveraging the instantaneous changes in the warp moisture content. Alsothere is disclosed Til in this embodiment the use or copper oxiderectifying means 48 in obtaining a source or direct current for theWheatstone bridge network from the commercial alternating current supplyconductors L and IF instead of from a battery 21 as disclosed in Fig. 3.It will be understood, however, that a battery 21 may be employed in thearrangement of Fig. 4, if desired and also that the rectifying means ofFig. 4 may be employed in the arrangement of Fig. 3.

As illustrated in Fig. 4, the resistance of warp I and resistance 39comprise one arm of a Wheatstone bridge network 2|a, which bridgenetwork may be exactly like the bridge network 2| of Fig. 3 except thatin lieu of the connection of resistance 25 and condenser 25 in seriesand shunting resistance 24 of the latter arrangement, a resistance 25ais connected in series with the resistance 24, and a condenser 26a isconnected in shunt to the resistance 25a. The output terminals of thecopper oxide rectifier l8 are connected to the energizing junctions 29and 30 of the bridge network 2|a and the input terminals of saidrectifier are connected to the terminals of the secondary winding .49 ofa transformer 50 having a line voltageprimary winding 5| connected tothe alternating current supply conductors L and L. No rebalancing meanshave been shown in Fig. 4 but it will be understood that a rebalancingaction of the bridge network 2|a may be eflfected in precisely the samemanner in which the bridge network 2| of Fig. 3 is rebalanced.

The resistance 25a and condenser 26a in this arrangement operate as dothe resistance 25 and network 2|a from being unbalanced in response toinstantaneous changes in warp resistance and pemiit the use of anextremely sensitive galvanometer 33 and also instantaneous rebalancingof the bridge network by adjustment of contact 32 along resistance 22.

In Fig. 5 I have illustrated, more or less diagrammatically a furthermodification of the measuring circuit arrangement of Fig. 3 in which anyunbalance of the Wheatstone bridge network 2| is not measured directlyby a galvanometer 33, but in which such unlalance is amplified by asuitable amplifier 52 to be described and the amplified quantity isapplied to the terminals of said galvanometer thereby obtaining greateraccuracy and sensitivity of measurement. As illustrated, the amplifier52 comprises a balanced Wheatstone bridge two adjacent arms of whichinclude balanced triode elements A and B respectively, of the hotcathodetype and pref verably contained in a single envelope C. The

other two bridge arms include resistances 53 and 54 respectively, inseries with the elements A and Band of equal value. The opposed normallyequlpotential junctions 55 and 56 of, the amplifier bridge are connectedby conductors 51 and 58 to the terminals of a galvanometer 33 whichgalvanometer may be identical to the correspondingly identified part ofthe Fig. 3 arrangement and has a shunt resistance 35 and a seriesresistance 31 associated therewith as in the latter arrangement. Theother two opposed junctions 59 and 6|] of the amplifier bridge areconnectedto a suitable source of direct current, which, in thisarrangement, comprises a power transformer 5| having a line voltageprimary winding 62 connected between the supply conductors L and L, andtwo high voltage sec ondary windings 63 and GI. One terminal of thesecondary winding 63 is connected to the anode of an indirectly heatedtype half wave rectifier valve D and the other terminal is connectedthrough a filtering condenser 61 to the cathode of said valve. Theterminal of condenser 6| which is connected to the cathode of valve D ispositive with respect to its other terminal and isconnected by aconductor 68 to the amplifier bridge terminal 59. The negative terminalof condenser 51 is connected by a conductor 59 to the amplifier bridgeterminal 50.

Energizing current is supplied the filament of valve D from thetransformer secondary winding 65 which winding also supplies energizingcurrent to the heating filament of a half wave rectifier valve E whichalso is of the indirectly heated type. Valve E supplies direct currentto the bridge network 2| and, as illustrated, has its anode connected toone terminal of the transformer secondary winding 64 the other terminalof which is connected through a filtering condenser Hi to the cathode ofsaid valve. The positive terminal. of condenser 10 is connected by aconductor H to the junction 30 of the bridge network H and the negativeterminal thereof is connected to the junction of said bridge.

As illustrated, the triodes A and B have a common cathode 12 which isheated by a filament l3 energized trom the transformer secondary winding66 and also include respective control electrodes 14 and I5 andrespective anodes l5 and IT. The anodes l8 and 11 are connected to thejunctions 55 and 55, respectively, and through the resistances 53 and 54to the positive terminal of condenser 61 and the cathode I2 is connectedthrougha biasing resistance I8 and conductors 35 and 58 to the negativeterminal of the condenser lil. The control electrode 14 is connected bythe conductor 35 to the junction 58, which Junction is connected to themovable contact 32 in engagement with the resistance '22, and thecontrol electrode 15 is connected to the junction 3| of bridge 2| by theconductor 34 in which a resistance 19 is inserted. 'In operation abiasing voltage is produced acrossthe resistance 18 in the cathodecircuit which renders the potential of the control electrode 14 negativewith respect to the potential of the cathode 12.

As previously indicated the triodes A and B should be balanced, ormatched, so that they have similar characteristics and to this end theyare both preferably contained ins-the same envelope C since the desiredidentity in characteristics of the triodes is more certainly insured byenclosing them in the same tube than if enclosed in separate tubes.

In operation with the normal balanced condition of the amplifier bridgecircuit shown in Fig. 5 the potentials of the control electrodes 14 and75 are similarly negative relative to the cathode 12 whereby the triodesA and B are equally conductive and the current flows through the bridgearm resistances 53 and 54 are equal and the bridge junction points and55 are therefore at the same potential and the pointer III of thealvanometer 33 will then be in its neutral or zero position. On adecrease in the moisture conthe increase in the value of the warpresistance results in an increased potential drop in the bridge armincluding the warp resistance and thus produces an unbalanced voltage inthe bridge circuit 2| to decrease the potential of the junc: tion -3|with respect to the junction 32 and theretent of the warp in contactwith the roller .of the control electrode 15 is negative relative to thecathode 12. This action operates to diminish the conductivity of thetriode B and makes the potential of the bridge junction 55 higher, or

In this arrangement, as in the previous arrangements described, onvariation in the value of warp moisture content the bridge network 2|may be rebalanced by adjustment of contact 32 relative to resistance 22.The contact 32 may be automatically adjusted as required for bridgerebalancing purposes by a relay mechanism under control of thegalvanometer pointer 40 and which may. be of the character employed toadjust the contact 32 of Fig. 3. As illustrated in Fig. 6, the generalcircuit provisions of Fig. 5 may be employed in a self balancingelectrical system not including a galvanometer, but in which therebalancing adjust ments of contact 32 are effected by a motor 42Acorresponding generally to the motor 42 of Fig. 3 but controlleddirectly from the amplifier 52 instead of through a galvanometer. Themotor 52A is connected in the output circuits of a pair of balancedtriode elements F and G which are preferably contained in a singleenvelope H and is selectively energized for rotation in one direction orthe other accordingly as the conductivity of one triode F or G isrendered different from the other in response to unbalance of bridge 2|.

The output circuits of the triodes A and B of the amplifier 52 which isresponsive to unbalance of bridge 2|, are coupled by the resistances 53and 54 to the input circuits of the triodes F and G. The triodes F and Gare illustrated as of the hot cathode type and as shown triode Fincludes an anode 80, a control grid 8|, a cathode I2 and a heaterfilament 83. The triode G includes the cathode I2 and heater filamentII, which elements are common to both trlodes F and G, and

also includes an anode 54 and a control grid 85. The heater filament 83is connected to a secondary winding 56a provided on the transformer 6|.and receives energizing .current therefrom.

Anode voltage is supplied the triodes F and G nal of transformersecondary winding 66b. The

other branch of the parallel network referred to includes the anodetocathode resistance of triode G and a winding 95 of motor 42A to theconductor 89 and the lower terminal of transformer secondary winding5622.

As illustrated, the motor 42A is of the induction variety and includesthree windings, namely the windings and 85 and a winding 9|, and

a squirrel cage rotor 52 with which two pairs of oppositely disposedfield poles (not shown) are associated. Winding 9| is wound on one pairof said field poles and windings II and 55 are I by to increase theextent to which the potential W n 0n he o h M D 1 one half 01' windingll being wound on a portion of one of the field poles which is adjacentthe rotor 82, and the other half being wound on portion of the otherpole remote from said rotor. Similarly, one half of winding 90 is woundon a portion of the last mentioned pole adjacent the rotor 82, and theother half of winding 90 is wound on a portion of the first mentionedpole remote from said rotor.

As illustrated, winding 8| is connected to the transformer secondarywinding 56b through a suitable condenser 93 so that the current whichflows through this winding will lead the voltage supplied by the winding56b by approximately 90. Winding 88 is energized by the currentfiowconducted by the triode F and the third winding 90 is energized by thecurrent flow conducted by the triode G. A condenser 94 of suitable valueis connected between the anodes 80 and 84 of the triodes F and G.windings 88 and 90 are so wound on motor 42A with respect to the mannerin which winding 9| is wound thereon that when they are equallyenergized rotor 92 will not be actuated for rotation in either directionbut will remain stationary. When one winding 88 or 90 is energized to agreater extent than the other, however, the rotor 82 will be actuatedfor rotation in a corresponding direction. That is to say, when. theanode to cathode resistance of triode F is approximately equal to anodeto cathode resistance of the triode G, the torque developed by winding88 for producing rotation of the rotor will be equal and opposite to thetorque developed by the winding 90 and accordingly the rotor will remainstationary. When the anode to cathode resistance of one valve G or F isdecreased or increased with respect to the other, however, the torquedeveloped by winding 90 with respect to that developed by winding 88will be increased and decreased, respectively, and the rotor 92 will beactuated for rotation in a corresponding direction.

By virtue of the connection of the output circults of triodes A and B tothe input circuits of triodes F and G, the anode to cathode resistanceof each of the latter triodes is controlled in accordance with theconductivity of the triodes A and B. The relative conductivities of thetriodes A and B, as explained previously in connection with thearrangement in Fig. 5, are controlled by the bridge network 2| so thaton unbalance of the latter in one direction, the triode B is renderedmore conductive than the triode A while on unbalance of the bridgenetwork in the opposite direction the conductivity of the triode B isdecreased with respect to that of the triode A. When the conductivitiesof the triodes A and B are the same, the conductivities of the triodes Fand G will be the same and consequently the motor "A will not beactuated for rotation in either direction and will remain .stationary.When the bridge network 2| is unbalanced in one direction or the other,however, the conductivity of triode B will be correspondingly increasedor decreased and accordingly the conductivity of the triode G will bedecreased or increased with respect to the conductivity of triode F toproduce rotation of the motor 42A in a corresponding direction;

- Fig. 7 discloses an alternative control arrangement to thatillustratedin Figs. 2 and 3. In Fig. 7, a reversible electrical motor423, which may be exactly. like the motor 42A of Fig.6, is shownconnected in parallel with motor 42A of Fig. 6 to directly operate thevalve III of Fig. 1.

In the forms of Figs. 3, 4 and 5 and without the control provisions ofFig. 2,.my present invention provides averaging means avoidingundesirable erratic measurements due to hunting," while coupled with thecontrol means of Figs. 2 or 7, hunting or oscillation of the control isminimized. The hunting elimination for the measurement purpose above isespecially desirable in the form of Fig. 6 wherein the inertia of therebalancing motor 42A would otherwise cause overtravel.

While in accordance with the provisions of the statutes I haveillustrated and described preferred embodiments of the presentinvention, those skilled in the art will understand that changes may bemade in the form of the apparatus disclosed without departing from thespirit of my invention as set forth in the appended claims, and thatsome features of the present invention may sometimes be used withadvantage, without a corresponding use of other features.

Having now described my invention, what I claim as new and desire tosecure by Letters Patent, is:

1. The method of measuring the value of a variable condition having thecharacteristic of normally fluctuating in magnitude about an averagevalue at a rate more rapid than the period 0? response of a measuringinstrument utilized in the measurement of the value of said condition.comprising the steps of producing an effect-in accordance with theaverage value of said condition during a predetermined time intervalwhich'time interval is of duration greater than the period of responseof said measuring instrument, opposing said effect to a second effect,measuring the difierence in magnitude between said first and secondmentioned efiects by means of said instrument, varying said secondmentioned effect in accordance with the measurement of said instrumentto reduce said difference substantially to zero, and measuring themagnitude of said second mentioned effect.

2. The method of measuring the moisture content of a moving web themoisture content of the successive portions of which normally fluctuatein magnitude about an average value at a rate more rapid than the periodof response of a measuring instrument utilized in the measurement of thevalue of the moisture content of said web comprising the steps ofmeasuringthe electrical conductivity of successive portions of said web,producing an effect in accordance with the average value of theelectrical conductivity of the successive portions of said web during apredetermined time interval which time interval is of duration greaterthan the period of response of said measuring instrument, opposing saideffeet to a second effect, measuring the difference in magnitude betweensaid first and second mentioned effects by means of said instrument,varying said second mentioned effect in accordance with the measurementof said instrument to reduce said difference substantially to zero, andmeasuring the magnitude of said second mentioned affect.

3. Apparatus for measuring the magnitude of a variable conditioncomprising a self balancing system adapted to be unbalanced on deviationof said variable condition from a predetermined value, means torebalance said system on unbalance thereof, means responsive to thestate of balance of said system to control said rebalancing means, andmeans included in said system to render said responsive meansunresponsive to transitory changes in the magnitude of said variablecondition without affecting the sensitivity of response of saidresponsive means to changes in the state of balance of said system.

4. Apparatus for measuring the magnitude of a variable conditioncomprising a self balancing system adapted to be unbalanced on deviationof said variable condition from a predetermined value, means torebalance said system on unbalance thereof, means responsive to thestate of balance of said system to control said rebalancing means, andmeans included in said system to render said responsive meansunresponsive to transitory changes in the magnitude of said conditionwithout affecting the operation of said rebalancing means in restoringthe balance of said system on unbalance thereof.

5. Apparatus for measuring the magnitude of a variable conditioncomprising a self balancing system adapted to be unbalanced on deviationof said variable condition from a predetermined value, means torebalance said system on unbalance thereof, means responsive to thestate of balance of said system to control said rebalancing means, andmeans included in said system to render said responsive meansunresponsive to transitory changes in the magnitude of said conditionwithout introducing delay in the rebalancing effect of operation of saidrebalancing means.

6. Apparatus for measuring the magnitude of a variable conditioncomprising a self balancing electrical network adapted to be unbalancedon deviation of said variable condition from a predetermined value,means to rebalance said network on unbalance thereof, means responsiveto the state of balance of said network to control said rebalancingmeans, and means having a connection with said network to render saidresponsive means unresponsive to transitory changes in the magnitude ofsaid condition without affecting the sensitivity of response of saidresponsive means to changes in the state of balance of said system.

7. Apparatus for measuring the magnitude of a variable conditioncomprising a self balancing electrical network adapted to be unbalancedon deviation of said variable condition from a predetermined value,means to rebalance said network on unbalance thereof, means responsiveto the state of balance of saidnetwork to control .said rebalancingmeans, and means connected to said network to render said responsivemeans unresponsive to transitory changes in the magnitude of saidcondition without affecting the operation of said rebalancing means inrestoringthe balance of said network on unbalance thereof.

8. Apparatus for measuring the magnitude of a variable conditioncomprising a self balancing electrical network adapted to be unbalancedon said network on unbalance thereof, means responsive to the state ofbalance of said network to control said rebalancing means and to controlthe adjustment of said exhibiting device, and means included in saidcircuit to render said responsive means unresponsive to transitorychanges in the conductivity of said substance without affecting thesensitivity of response of said responsive means to unbalance of saidnetwork. w

10. Apparatus for measuring the conductivity of a substance including anadjustable exhibiting device, a self balancing electrical networkadapted to be unbalanced only on sustained deviation of the conductivityof said substance from a predetermined value, means to rebalance saidnetwork on unbalance thereof, means responsive to the state of balanceof said network to control said rebalancing means and to control theadjustment of said exhibiting device, and means included in said circuitto render said responsive means unresponsive to transitory changes inthe conductivity of said substance without affecting operation of saidrebalancing meansv in restoring the balance of said network on unbalancethereof. I

11. Apparatus for measuring the conductivity of a substance including anadjustable exhibiting device, a self balancing electrical networkadapted to be unbalanced only on sustained deviation of the conductivityof said substance from a predetermined value, means to rebalance saidnetwork on unbalance thereof, means responsive to the state of balanceof said network to control said rebalancing means and to control theadjust- 12. Apparatus for measuring the magnitude of a variablecondition comprising a self balancing electrical network adapted to beunbalanced on deviation of said variable condition from a predeterminedvalue, means to rebalance said network on unbalance thereof, meansresponsive to the state of balance of said network to control saidrebalancing means, and means connected to said network to render saidresponsive means unresponsive to transitory changes in the magnitude ofsaid condition without affecting the sensitivity of response of saidresponsive means and without affecting the operation of said rebalancing means in restoring the balance. of saidnet work on-unbalancethereof.

13. Apparatus for measuring the moisture content of a moving webincluding an adjustable exhibiting device, a normally balancedelectrical network adapted to include the electrical resistance'ofsuccesive portions of said web therein and adapted to be unbalanced ondeviation in the average resistance of said web from a predeterminedvalue, means to rebalance said network on unbalance thereof, meansresponsive to the state of balance of said network to control saidrebalancing means and to control the adjustment of said exhibitingdevice, and means included in said network to renderv said responsivemeans unresponsive to substantial differences in the electricalresistance of adjacent portions of said web without affecting thesensitivity of response of said responsive means to unbalance of saidnetwork.

14. Apparatus for measuring the moisture content of a moving webincluding an adjustable exhibiting device, a normally balancedelectrical network adapted to include the electrical resistance ofsuccessive portions of said web therein and adapted to be unbalanced ondeviation in the average resistance of said web from a predeterminedvalue, means to rebalance said network on unbalance thereof, meansresponsive to the state of balance of said network to control saidrebalancing means and to control the adjustment of said exhibitingdevice, and means included in said network to render said responsivemeans unresponsive to substantial differences in the electricalresistance of adjacent portions of said web without affecting theoperation of said rebalancing means in restoring the balance of saidnetwork on unbalance thereof.

15. Apparatus for measuring the moisture content of a moving webincluding an adjustable exhibiting device, a normally balancedelectrical network adapted to include the electrical resistance ofsuccessive portions of said web therein and adapted to be unbalanced ondeviation in the average resistance of said web from a predeterminedvalue, means to rebalance said network on unbalance thereof, meansresponsive to the state of balance of said network to control saidrebalancing means and to control the adjustment of said exhibitingdevice, and means included in said network to render, said responsivemeans unresponsive to substantial differences in the electricalresistance of adjacent portions of said web without atl'ecting thesensitivity of response of said responsive means on unbalance of saidnetwork and without aflecting the operation of said rebalancing means inrestoring the balance of said network on unbalance thereof.

16. Apparatus for measuring the magnitude of a variable conditionincluding an adjustable exhibiting device, a normally balanced systemadapted to be unbalanced on deviation in the magnitude of said conditionfrom a predetermined value, means responsive to the state of balance ofsaid system to control the adjustment of said exhibiting device, andmeans included in said system to render said responsive meansunresponsive to transitory changes in the magnitude of said conditionwithout affecting the sensitivity of response of said responsive meansto unbalance of said system.

l7.' Apparatus for measuring the moisture content of a moving webincluding an adjustable exhibiting device, a normally balancedelectrical network adapted to include the electrical resistance of saidweb'therein and adapted to be unbalanced on deviation in the averageresistance' of said web from a predetermined value, means responsive tothe state of balance of said network to control the adjustment of saidexhibiting device, and means included in said network to render saidresponsive means unresponsive to transitory changes in the electricalresistance of said moving web without affecting the sensitivity ofresponse of said responsive means.

18. Self balancing apparatus including an network when the latter isunbalanced due to deviation in said variable resistance from apredetermined value, means responsivie to unbalance of said bridgenetwork for adjusting said adjustable resistance to rebalance saidnetwork, and means included in said bridge network to render saidresponsive means unresponsive to transitory changes in the value of saidvariable resistance without affecting the sensitivity of response ofsaid rebalancing means to unbalance of said bridge network.

19. Self balancing apparatus including an electrical bridge network onearm of which includes a resistance the magnitude of which varies inaccordance with the magnitude of a variable condition and the other armsof which include other resistances, one of said other resistances beingadjustable to rebalance said bridge network when the latter isunbalanced due to deviation in said variable resistance from apredetermined value, means responsive to unbalance of said bridgenetwork for adjusting said adjustable resistance to rebalance saidnetwork, and means included in said bridge network to render saidresponsive means unresponsive to transitory changes in the value of saidvariable resistance without introducing delay in the rebalancing effectof adjustment of said adjustable resistance.

20. Self balancing apparatus including an electrical bridge network onearm of which includes a resistance the magnitude of which varies inaccordance with the magnitude of a variable condition and the other armsof which include other resistances, one of said other resistances beingadjustable to rebalance said bridge network when the latter isunbalanced due to deviation in said variable resistance from apredetermined value, means responsive to unbalance of said bridgenetwork for adjusting said adjustable resistance to rebalance saidnetwork, and means to stabilize the operation of said last mentionedmeans including capacitative means connected in said bridge network andadapted to render the latter unresponsive to transitory changes in thevalue of said variable resistance.

21. Self balancing apparatus including a normally balanced electricalnetwork, a plurality of impedances included in said network one of whichvaries in magnitude in accordance with the variations in magnitude of avariable condition, another one of said impedances being adjustable torebalance said network when the latter is unbalanced due to deviation insaid variable impedance from a predetermined value, means responsive tounbalance of said network for adjusting said adjustable impedance, andmeans to stabilize the operation of said last mentioned means includingcapacitative means adapted to render said network unresponsive totransitory changes in the value of said variable impedance withoutaffecting the sensitivity of response of said responsive means.

22. Apparatus for measuring the conductivity of a variable resistanceincluding an exhibiting device, an electrical bridge network having apair of balancing junctions and including said variable resistance inone arm thereof and adapted electrical bridge network one arm of whichto be unbalanced on deviation in said variable cludes a resistance themagnitude of which varies in accordance with the magnitude of a variablecondition and the other arms of which include other resistances, one ofsaid other resistresistance from a predetermined value, connectionsbetween said balancing junctions of said bridge network and saidexhibiting device, and means included in another arm of said bridgeances being adjustable to rebalance said bridge 76 network to render thelatter insensitiv to tramtory changes in the value of said variableresistance.

23. Apparatus for measuring the conductivity of a variable impedanceincluding an electrical current responsive device, a Wheatstone bridgenetwork including said variable impedance in one arm thereof and adaptedto be unbalanced on deviation in said variable impedance irom apredetermined value, connections between the balancing junctions of saidbridge network and said current responsive device, and means included inanother arm of said bridge network to render the latter insensitive totransitory changes in the value of said variable impedance.

24. Apparatus for measuring the conductivity of a variable resistanceincluding electrical current energizing means, an electrical bridgenetwork energized by said means and having said variable resistanceincluded in one of its arms and other resistances in its remaining arms,one of said other resistances being adjustable to rebalance said bridgenetwork when the latter is unbalanced due to deviation in said variableresistance from a predetermined value, means responsive to unbalance ofsaid bridge network for adjusting said adjustable resistance, and meansconnected to another one of said other resistances adapted to render thesaid bridge network insensitive to transitory changes in the value ofsaid variable resistance.

25. The combination of claim 24 wherein the said last mentioned meansincludes a condenser connected in shunt to at least a portion of saidanother one of said other resistances.

26. The combination of claim 24 wherein the said dast mentioned meansincludes a condenser and a resistance in series connected in shunt to atleast a portion or said another one of said other resistances.

27. The combination or claim 24 wherein the said last mentioned means donot affect the operation of said bridge rebalancing means in restoringthe bridge network balance on unbalance plify the unbalance of saidbridge networkand,

having an input circuit and an output circuit connections between thebalancing Junctions 01' said bridge network and the input circuit ofsaid amplifier, connections between the said current responsive deviceand the output circuit of said amplifier, and means included in anotherarm of said bridge network adapted to render the latter insensitive totransitory changes in the value of said variable impedance.

29. Apparatus for measuring the conductivity of a v'ariable resistanceincluding an electrical current responsive device, a Wheatstone bridgenetwork including said variable resistance in one arm thereof andadapted to be unbalanced on deviation in said variable resistance from apredetermined value, an electronic amplifier to amplify the unbalance ofsaid bridge network and having an input circuit and an outputcircuit,connections between the balancing junctions of said bridge network andthe input circuit of said amplifier, connections between the saidcurrent responsive device and the output circuit or said amplifier, anda condenser included in another arm of said bridge network to render thelatter unresponsive to transitory changes in the value 01' said variableresistance.

HARRY S. JONES.

